Instead, Rubio came in a very strong third — a third that was very nearly second, as he crept up on Trump's vote total. In Monday's Iowa GOP caucuses, Cruz got 28 percent of the vote, Trump 24 percent and Rubio 23 percent.
Rubio came within a couple hundred supporters of piercing the impenetrable bubble thought to be around Cruz and Trump — and on the two leaders' own political turf, no less. He over-performed expectations, and for that, Rubio perhaps almost as much as Cruz can call Monday a win.
A few minutes after the Associated Press called the race for Cruz, Rubio took the stage in Iowa, flanked by his family. But if you were listening to Rubio's speech in a news vacuum, you would have thought AP called the race for him.
"For months, they said we had no chance," he said. "… They told me I had no chance because my hair wasn't gray enough and my boots were too high."
Then, he pivoted to what can only be described as a general election stump speech — sharing his Cuban immigrant parents' story of making it in America, knocking Democrat Hillary Clinton for her emails and warning that "everything that makes this nation great now hangs in the balance" of this presidential election.
Rubio's impressive results in the Iowa caucus — and his speech afterward — were tailored to one simple message: He is the GOP candidate with the broadest appeal to win in a general election, and Iowa proves it.
"We are going to unify this party, and we are going to unify the conservative movement," he said Monday, a subtle dig at both Cruz's and Trump's reputation for divisiveness.
Rubio is arguing that Iowa is proof that his strategy, to be many things to many different people, is working. He was never expected to win among such a conservative electorate, so the fact he got so close to the two who were — even after going on the defense for supporting immigration reform in 2013 — suggests he has staying power among the social conservative community while he carries the mantle of leader of the establishment pack. (The next establishment candidate, former Florida governor Jeb Bush, came in sixth place Monday with 3 percent of the vote.)
Still, one great night does not a nomination make.
There are some holes in his argument, like Rubio's support in Iowa may not be as widespread as he indicates. He won support in Iowa's metropolitan areas, where voters tend to be more moderate, and didn't appear to win a single other.
And Rubio is going to need whatever momentum Iowa gives him for the next contest, New Hampshire's primary. There, a more moderate state that should be more in Rubio's wheelhouse, he is fifth and has been criticized for not campaigning very hard.
Daring to look even further ahead, Rubio is in a familiar position in South Carolina: Third behind Trump and Cruz. But we'll note that, as Iowa votes were being tallied, Politico reported the well-liked Sen. Tim Scott (R-S.C.) is expected to endorse Rubio in his state's primary. And there, Rubio's good night became even better.
Time will tell whether Rubio's strong Monday night will be a turning point for his campaign. But for now, he's the candidate whose showing was probably the biggest surprise of the Iowa caucuses.